The present invention relates to a bicycle brake assembly which is used in conjunction with the hub of a bicycle and, more particularly, to a brake assembly which includes a rotary body screwed onto the mounting tube of a wheel hub, the hub further including a hub shaft secured to the frame of the bicycle and a hub shell rotatably supported thereon. The hub shell comprises a pair of flanges and at least one mounting cylinder provided with screw threads on the outer periphery thereof which forms the mounting tube.
In this type of brake assembly, the rotary body engages via a screw coupling with the mounting tube on the hub and is adapted to rotate together with the hub. A braking member is further provided having a contact face which comes into contact against the rotary body to stop its rotation.
The fundamental construction of this brake assembly is already known and is found in three different types of braking mechanisms. In a first type of braking mechanism, the rotary body is a drum and the braking member is composed of a pair of brake arms extending around the periphery of the drum. An operating arm pulls the brake arms towards the rotary body where brake pads contact the drum. A second known braking mechanism is the band brake wherein the braking member is composed of a brake band which is pulled toward the rotary body by an operating lever to engage with the rotary body. A third type of braking mechanism is the disc brake wherein the rotary body is a disc and the braking member is composed of a pair of pads, a caliper body supporting these pads, and an operating means for moving one of the pads into contact with the disc.
In the three types of braking mechanisms just described, the rotary body is screwed onto the mounting tube of the hub to rotate together with the hub. During the braking operation in the forward running of the bicycle, the braking torque applied to the rotary body causes it to rotate relative to the mounting tube in a direction towards the tightening of the rotary body on the mounting tube thereby preventing the rotary body from being loosened. However, during the braking operation in the rearward running of the bicycle, the braking torque works in an opposite direction which tends to unscrew or loosen the rotary body from the mounting tube.
To counteract the tendency for the rotary body to loosen from the mounting tube, a lock nut is generally provided. However, unless some type of sufficient clamping is provided when the rotary body is engaged with the mounting tube, the rotary body may become loose even when the lock nut is present. This is because without sifficient clamping between the rotary body and mounting tube, the rotary body receives braking torque through the braking operation during the forward running of the bicycle and is therefore screwed tighter on the mounting tube. This produces a gap between the rotary body and the lock nut causing the lock nut to loosen whereby it may become disengaged from the rotary body due to the vibrations occurring during the normal bicycle operation. Thus, during the braking operation in the rearward running of the bicycle, the rotary body may become disengaged from the mounting tube or, at least, noise may be generated as the rotary body again contacts the lock nut if the rotary body cannot loosen to the point of becoming disengaged from the mounting tube.
The present invention provides a brake mechanism for a bicycle which overcomes the problems of a loose rotary body. An object of the present invention is to provide a brake mechanism of simple construction, which dispenses with the lock nut but yet does not allow for a loosening of the rotary body from the mounting tube even if braking torque is applied during rearward running of the bicycle. To this end, a coil spring, which has its diameter reduced by rotation of the rotary body in the loosening direction, i.e., counter to the screwing direction, is mounted on the rotary body. When the rotary body is in engagement with the mounting tube, the inner peripheral face of the coil spring is brought into pressure contact against the outer peripheral face of the hub mounting tube.
The coil spring not only reduces its diameter upon application of force along its screwing direction, it also expands its diameter upon application of force along the direction opposite to the screwing direction. Consequently, the coil spring fastens itself on the rotary body with a large force during the reduction of the coil spring diameter. The coil spring action is used to reliably prevent the rotation of the rotary body in its unscrewing direction without reliance on a lock nut, and the screwed engagement of the rotary body with the mounting tube is positively retained by the fastening action of the coil spring during the diameter reduction. On the other hand, the coil expands to permit rotation of the rotary body in a direction of tightening itself on the mounting tube.
These and other objects of the present invention will be apparent from the embodiments described below in accordance with the accompanying drawings.